Study says hot summer temperatures won’t curb spread of COVID-19 after all

“Summer is not going to make this go away.” 

Those are the sobering words of Professor Dionne Gesink, co-author of a new coronavirus study just released by the University of Toronto. Canadian researchers have concluded that neither temperature nor latitude influences the spread of coronavirus. Many people have been hopeful that scorching summer temperatures will help stop COVID-19, but this new research has conclusively shut the door on that possibility.

It’s deflating, no doubt, but the study’s authors also have some promising findings to report as well. While the temperature may not make a dent in the coronavirus’ presence, their research indicates that public health measures, such as school closures and social distancing, are significantly slowing COVID-19 down all over the planet.

“Our study provides important new evidence, using global data from the COVID-19 epidemic, that these public health interventions have reduced epidemic growth,” comments Dr. Peter Jüni, from the Institute for Health Policy, Management and Evaluation, University of Toronto, and St. Michael’s Hospital, Toronto, Ontario.

“If we open schools too soon or without appropriate measures to control the pandemic it could backfire big time,” he explains in a university release. “Countries that closed schools quickly are faring better on average than those that didn’t – with climate playing no role. Our research suggests warming weather should not be a factor in the decision to reopen schools.”

The research team analyzed 144 geopolitical regions spanning the globe, from Australia and Asia to Europe and North America. In all, over 375,000 confirmed COVID-19 infections were investigated for this study. In fact, this is the first peer-reviewed project from outside of China to conclude temperature and climate don’t affect coronavirus transmission. However, China, Italy, South Korea, and Iran weren’t included because those nations were either largely recovering from the virus at the time of the research or amid a full-blown outbreak.

To estimate the virus’ spread, the study’s authors compared infection rates from March 20th to March 27th in various areas. This was done to establish the influence of a variety of factors on COVID-19’s spread; school closures, humidity, social distancing rules between March 7th-13th, bans on mass gatherings, latitude, and temperature.

To examine the effect of climate specifically, the time surrounding the Spring equinox was studied. During each annual Spring equinox, the sun’s rays reach both of Earth’s hemispheres equally. This allowed researchers to account for latitude and temperature simultaneously in various major cities, and then cross-reference that data with other lockdown and health measures.

After finishing their research, the study’s authors found little to no association between latitude or temperature and the spread of COVID-19. Moreover, there was a weak association noted between humidity and COVID-19’s growth.

As far as why humidity appears to slightly impede the coronavirus, it’s theorized that viral aerosol droplets fall faster when it’s humid. Viral particles are also known to become less stable in heavy, wet air. Unfortunately, according to the study, the benefits of humidity pale in comparison to social distancing.

Even the researchers themselves say they were surprised by what they found. 

“We had conducted a preliminary study that suggested both latitude and temperature could play a role,” Dr. Jüni says. “But when we repeated the study under much more rigorous conditions, we got the opposite result.”

If you aren’t convinced by the science behind these findings, consider the different approaches and outcomes of two countries: Greece and Singapore. Despite having a much hotter and more humid climate than Greece, Singapore is dealing with about 10 times more COVID-19 cases than Greece. Why? While Greece shut down schools quickly after its first confirmed case, Singapore waited months.

So, why is COVID-19 impervious to warm weather even though the flu largely disappears each Spring? The difference, according to Dr. Jüni, is that most people are already partially immune to the flu. Flu immunity has gradually been building over the years thanks to vaccinations and people simply becoming sick and recovering. When the flu roars back every Fall, that’s due to new mutations and the onset of colder weather. The coronavirus, on the other hand, “doesn’t need favorable conditions to thrive because people have no immunity to it.”

It’s imperative that everyone, from average citizens to legislators and decision-makers, realize that the coronavirus isn’t going to magically disappear by August, as much as we all would love for that to happen. 

“The more public health interventions an area had in place, the bigger the impact on slowing the epidemic growth. These public health interventions are really important because they’re the only thing working right now to slow the epidemic,” notes Professor Gesink.

Lockdowns and social distancing can’t last forever, though, which is why these findings represent a major conundrum. Everyone’s mental health is hurting right now, and the global economy needs to recover. There’s no easy answer here, but before we can beat COVID-19 we have to fully understand it. As disappointing as it is that summer won’t slow the virus down, at least now we know.

The full study can be found here, published in the Canadian Medical Association Journal.

John Anderer is a frequent contributor to Ladders News.